The present invention relates generally to disc drives. More particularly, the present invention relates to a method and apparatus for balancing a disc stack assembly of a disc drive.
In a typical disc drive, data storage or retrieval involves positioning a read/write head over the relevant disc surface when the disc is spinning. The discs are therefore mounted on a spindle motor, one disc on top of another, separated by spacers, to form a disc stack assembly.
It is important to provide a suitable disc clamp to secure the various components of the disc stack assembly so that the components remain in alignment to each other under high speed rotation, and even in the presence of a high external shock. Ideally, a disc clamp should provide the required clamping forces on a disc evenly so as to minimize disc warpage. Accordingly, disc clamps are generally designed to be rotationally symmetrical.
As the disc stack assembly is required to rotate at high speeds, it is also essential to minimize any imbalance so as to avoid excessive vibrations. Imbalance in a disc stack assembly can result in track mis-registration and erratic speed variations, which in turn causes read/write errors.
One method of correcting imbalance involves fixing the discs so that they are alternately shifted in diametrically opposite directions, as disclosed in the U.S. Pat. No. 4,683,505 issued Jul. 28, 1987 to Schmidt et al. This method is however not suitable for use with disc stack assemblies having only one disc or an odd number of discs.
Another method of correcting imbalance involves mounting an additional component to the disc stack assembly so as to provide a counter-balancing weight. For example, in the U.S. Pat. No. 5,555,144 issued Sep. 10, 1996, Wood et al. discloses the use of a C-shaped balancing clip which can be added to the disc stack assembly and positioned in an appropriate orientation to provide the desired counter-balance. Alternatively, the counter-balance may be introduced by the use of a spacer ring which has part of its edge machined off so that its center of gravity is offset from the center of the spacer ring. Generally, it is desirable to reduce the number of components so as to improve manufacturing efficiency. Therefore, in cases where there is only one disc in the disc stack assembly and spacers are not required, it is preferred if the use of such a spacer ring can be avoided.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention relates to a disc drive component which incorporates two seemingly incompatible functions of clamping a disc stack assembly and balancing the disc stack assembly.
The disc stack assembly is designed to rotate about an axis of rotation. When the disc clamp is secured to the spindle motor at the one or more attachment points so that the center of the disc clamp substantially coincides with the axis of rotation, and clamping forces are exerted on the disc stack assembly. The various components of the disc stack assembly can thus be clamped in fixed position relative to one another. The disc clamp includes two or more openings, one or more of which has a flange extending into the opening. The number of flanges, and the size and shape of each flange are varied such that the center of gravity of the disc clamp is offset from the center of the disc clamp. The arrangement is such that, disregarding the flanges, the disc clamp has rotational symmetry about the center, but taking the flanges into consideration, the disc clamp is rotationally asymmetrical about the center.
Traditionally, it is expected that a disc clamp that does not have rotational symmetry will exert uneven clamping forces and therefore cause disc warpage. Therefore, conventional balancing methods have been limited to the use of other additional components to provide the counter-balancing weight to the disc stack assembly, and conventional disc clamps are designed to have rotational symmetry. The disc clamp of the present invention is however able to provide a counter-balancing weight to a disc stack assembly while at the same time provides an evenly distributed clamping force.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.